This may be what their intention is, but it is not what their license terms actually state.  This is a common incorrect interpretation that open source use is not a commercial use.  Especially under US law (and most jurisdictions that come to mind), it very much is a commercial activity, even if no money is involved (but money could be involved too).  CC-BY-NC is a no-go.

If they are okay with open source projects using their charts, then they should state that (by licensing under a standard open source use license like CC-BY or even GPL).

Thanks for the clarification. I thought if we had a go-ahead from them, then we could use it but I was clearly wrong. Moving to a different library should not be a problem but my only concern is it would push back the schedule by a few days. I am done with the initial charts using HighCharts.js, and migrating them might take some time, so please be patient. :)

Please compare libraries within boundaries set, to make a better
choice for this project.

I will look into the other libraries again and try to pick an alternative as soon as possible.